Positioning of mechanical systems, robots, aircraft, and spacecraft may be accomplished by a variety of means, including mechanical or optical encoders, video cameras, radar, ultrasonic, and laser ranging systems. To measure the position and orientation of a rigid object, or a sensor attached to the rigid object, a direction to four or more optical targets fixed to a reference object must generally be measured. Sensors such as charge coupled devices, video camera or position sensing detectors may be used to detect the optical targets.
Position sensing detectors are analog devices that centroid incoming light energy sources to determine the direction and position of the optical targets. One example of a position measurement system utilizing position sensing detectors includes placing three or more reflective targets on a target object whose position and orientation is to be measured. Light beams are directed toward the optical targets and produce reflected beams. Each reflected beam is received by a position sensing detector, such as a lateral-effect photodiode. The signals generated by the position sensing detectors are used to determine measurements of translation along and rotation about three non-parallel axes which define the space in which the target object moves.
Prior position measurement systems and methods suffer several disadvantages. For example, the applications of the position measurement systems are generally restricted due to the necessity that retro-reflectors be positioned on an object which is essentially non-reflective. Additionally, any other objects in the measurement system environment must also be essentially non-reflecting.
Additionally, charge coupled devices and video cameras generally require post-processing of a relatively large quantity of digitized image data, in the form of digitized pixel response, to recognize and numerically centroid the optical target images. This process is generally computationally expensive and difficult in the presence of geometrical and environmental variations.